The renin-angiotensin system is involved in the homeostatic function to control systemic blood pressure, the volume of body fluid, balance among the electrolytes, etc., associated with the aldosterone system. Development of angiotensin II converting enzyme inhibitors (ACE inhibitor) (this converting enzyme produces angiotensin II which possesses a strong vasoconstrictive action) has clarified the relation between the renin-angiotensin system and hypertension. Since angiotensin II constricts a blood vessel to elevate blood pressure via the angiotensin II receptors on the cellular membranes, angiotensin II antagonists, like the ACE inhibitor, would be useful in treating hypertension caused by angiotensin. It has been reported that various angiotensin II analogues such as saralasin, [Sar.sup.1, Ala.sup.8 ]AII, and the like, possess potent angiotensin II antagonist activity. It has, however, been reported that, when peptide antagonists are administered parenterally, their actions are not prolonged and, when administered orally, they are ineffective [M. A. Ondetti and D. W. Cushman, Annual Reports in Medicinal Chemistry, 13, 82-91(1978)].
On the other hand, for solving the problems observed with these peptide antagonists, studies on non-peptide angiotensin II antagonists have been - conducted. In the earliest studies in this field, imidazole derivatives having angiotensin II antagonist activity have been disclosed in Japanese Patent Unexamined Publication Nos. 71073/1981, 71074/1981, 92270/1982, and 15768/1983, U.S. Pat. Nos. 4,355,040 and 4,340,598, etc. Later, improved imidazole derivatives were disclosed in EP-0253310, EP-0291969, EP-0324377, and Japanese Patent Unexamined Publication No. 23868/1988 and Japanese Patent Unexamined Publication No. 117876/1989. And, as angiotensin II antagonists, pyrrole, pyrazole and triazole derivatives are disclosed in EP-0323841 and Japanese Patent Unexamined Publication No. 287071/1989, while benzimidazole derivatives are disclosed in U.S. Pat. No. 4,880,804.